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Morning all

New to solar but been in the electrical field a while. A couple of very basic questions if anyone willing to help? 

I done an install, the equipment was purchased and supplied by others so had no input into that.

Setup

1 x 5kva Mecer inverter

1 x Dyness B4874 battery

12 x 335watt panels (4 strings of 3)

Question

What kind of max wattage would we likely to get out of those panels on an average winters and summers day lets say between 10h00 and 15h00(i know that it is better to work on KWh, also know that wiring size and a couple other factors etc comes into effect) but just asking from your guys experience. 

What kind of losses (wattage of panels) should we expect on average, if the setup is done perfectly, (read somewhere that if its a perfect summers day at 12h00 and panel angle is perfect as well as positioning) you are only likely to get 80% of total output, is that correct? 

Got a couple more basic questions, will ask once i get my head around a few matters. 

Thanks guys

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2 hours ago, Walkervillian said:

What kind of max wattage would we likely to get out of those panels on an average winters and summers day lets say between 10h00 and 15h00(i know that it is better to work on KWh, also know that wiring size and a couple other factors etc comes into effect) but just asking from your guys experience. 

I have learned that as a general rule of thumb you can expect 5x your installed PV capacity as total output on normal (non-cloudy) days. So in your case that would be 5*12*335 = 20kWh. This of course is based on the assumption that you have sufficient loads to consume the production and that your MPPT does not throttle due to insufficient loads.

As an example, my system has too much PV at the moment and around 13h30 my batteries are already fully charged, after which the MPPT throttles back. So even though I should expect around 23kWh from my system, I am only getting around 18kWh. Once my extra Pylon battery finally arrives, my system should be better balanced and I should be getting closer to maximizing my PV potential every day.

2 hours ago, Walkervillian said:

What kind of losses (wattage of panels) should we expect on average, if the setup is done perfectly, (read somewhere that if its a perfect summers day at 12h00 and panel angle is perfect as well as positioning) you are only likely to get 80% of total output, is that correct? 

80% as general rule for max average output is correct. You will have hotter days on which you will not achieve that and you will have colder days on you will get higher output. You will also get short peaks where your production might be above your installed capacity 

3 hours ago, Walkervillian said:

Setup

1 x 5kva Mecer inverter

1 x Dyness B4874 battery

12 x 335watt panels (4 strings of 3)

Some questions/remarks in return:

  • The Dyness is a 3.5kWh module, correct? If yes, then this would be very light compared to your installed PV capacity and you would most likely have the same scenario I described above
  • Depending on the specs of your panels and the MPPT in the Mecer, you might be getting very close to (or even beyond) the point where the Mecer starts derating the PV input
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Hi

Thanks for feedback, makes sense, I have already suggested to client to increase battery setup. From what i understand the dyness has a 3.2kw storage, it can only discharge at 1,68kw

Next question would of been what happens to excess solar power if load is minimal, but think you have already answered that, the mecer (mppt) limits or "throttles" it, is that correct? 

How does the Mecer rate compared to other invereters especially when it comes to switching, (from utility to solar, or vice versa, utilising battery when solar is not sufficient and so forth. 

Thanks

 

 

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6 hours ago, Walkervillian said:

From what i understand the dyness has a 3.2kw storage, it can only discharge at 1,68kw

I do not know the Dyness at all, but this sounds a bit low. I would assume 80% DOD, which would mean 2.56kWh available for use

6 hours ago, Walkervillian said:

Next question would of been what happens to excess solar power if load is minimal, but think you have already answered that, the mecer (mppt) limits or "throttles" it, is that correct? 

Correct. The MPPT will throttle back to whatever power is required by the loads

6 hours ago, Walkervillian said:

How does the Mecer rate compared to other invereters especially when it comes to switching, (from utility to solar, or vice versa, utilising battery when solar is not sufficient and so forth. 

It works ;-) The biggest problem of the Mecer (or Axpert) in this regard is that it cannot communicate with an external BMS and works on it's own voltage measurement of the battery to determine when to switch, which might in reality be significantly different to the actual SOC of the battery. The software ICC offers a work-around for that as it is able to communicate with some BMS's (not sure if Dyness is among them) as well as a Victron BMV, which can otherwise be used to determine the SOC of a battery. ICC then switches the Mecer/Axpert between Utility and SBU based on that SOC data, which is much more accurate. That is what I am using in my own system and am very happy with

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Thanks Wolfandy

So it seems its probably better not to use batteries with BMS on the Mecer units. 

Have you ever found that the mecer/axpert PV input goes to 0 watts but still shows the voltage, it stays in this state until PV is isolated and then re-instated before it produces power again, what would cause this? 

 

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5 hours ago, Walkervillian said:

So it seems its probably better not to use batteries with BMS on the Mecer units. 

There is no downside to doing so. But you will not be able to have the Mecer/Axpert directly communicate with the BMS. The upside that you do get from the BMS is the additional protection of the BMS against abuse of the battery (e.g. overcharging or depleting below safety limit).

I am running Pylontech batteries with built-in BMS (to my understanding similar to your Dyness) with my Mecer/Axperts and the system runs great (but with ICC controlling the system)

5 hours ago, Walkervillian said:

Have you ever found that the mecer/axpert PV input goes to 0 watts but still shows the voltage, it stays in this state until PV is isolated and then re-instated before it produces power again, what would cause this? 

As @plonkster has explained to me in this thread, "it is the MPPT doing a rescan to see if it can find a better power peak". His explanation is on a Victron MPPT, but the same holds true for the Mecer/Axpert MPPT. When I had my PV directly connected to the Mecer/Axperts, I would have the same phenomenon - just less frequent than on the Victron MPPT

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12 hours ago, wolfandy said:

MPPT doing a rescan

It should not get stuck at zero for any length of time though.

MPPTs have different ways of handling this, but it usually happens when the MPPT has been running limited for a while, and is then suddenly called upon to provide full power. While running limited it was by definition running off of the maximum power point, so this event calls upon it to go forth and seek the maximum power point (yet again). By far the simplest way to do that is to scan the whole range, that is, start from zero (which will show the maximum PV voltage) and then load it down. This should take at most a few seconds, and it should settle on the maximum within 30 seconds.

The Victron chargers don't start from zero. They start from wherever they are, and they split the scan up into three parts. So you never lose power completely, you just see these three short dips.

If you lose power completely and it won't restart until you've removed and restored the PV power, something else is wrong.

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Thanks Gents, 

Makes sense, this event of 0 watts but still reflecting voltage has happened on maybe 2 occassions in about 5 weeks, knowing the load it is minimal for extended periods and then does require more at certain stages, maybe that the cause. 

According to owner itvhas to be "reset" beforr it produces power again. 

If not what else could you guys suggest i check

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On 2020/05/27 at 11:04 AM, Walkervillian said:

According to owner itvhas to be "reset" beforr it produces power again. 

Sometimes the MPPT can get stuck on the wrong point. I've seen this twice now, once was actually in Norway, so far up North that you get days where the sun comes up in the east, swings around in a flat line across the horizon in a half-circle and then sets again 22 hours later, leading to ridiculously long solar days but not much insolation.

In any case, I've seen it get stuck on a tiny blip very high up on the voltage scale, causing it to make less than a watt, so it looks like the MPPT has simply stopped, while in reality it is tracking a maximum... the wrong one.

20 years ago I did a course in optimisation, in which this issue was discussed (locking on to a "local" maximum). If the constraints are not linear, that sort of thing can  happen.

(It also happens to be why I don't buy the philosophical idea of a "moral landscape", where if you see something work well you just do more of it until you reach a utopia... cause I already know that kind of algorithm only finds local maximae 🙂. How's that for a bit of Friday OT-ness!).

Edited by plonkster
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